Systems for controlling air pollution today typically utilize chemical compounds to combine and/or react with the contaminant or contaminants of interest to form compounds or other chemical structures that may be removed from the system being controlled. While such chemical air pollution control systems are useful in controlling and reducing air pollution, it becomes apparent from a thorough study and review of such systems that they are inherently inefficient, often quite expensive in that they require large capital outlay, generate large quantities of waste material, and are awkward and difficult to adapt and install into existing effluent gas systems.
For example, one conventional means of controlling sulfur dioxide in fossil fuel fired power plants today is the system commonly referred to as a wet limestone scrubbing system. In such a system, limestone and water are introduced to the flue gases being emitted from the boiler, resulting in the formation of what is referred to as sludge. During the continuous operation of such a system, the deposit of sludge (calcium sulfate and calcium sulfite) grows and one is confronted with the problem of removing large masses of accumulated sludge. For instance, for a 100 MW coal fired power plant, it can be expected that over a twelve month period, 100,000 to 1,000,000 tons of sludge will result and require removal from the site of deposit. This, of course, presents a tremendous material handling and disposal problem and is most certainly one of the principal disadvantages to the wet limestone scrubbing technique for removing sulfur dioxide from the flue gases associated with fossil fuel fired power plants.
With the wet limestone control system, the sulfur dioxide removal efficiency falls within the 70 to 90 per cent range. However, the wet limestone control system is principally aimed at controlling the emission of sulfur dioxide, and does not effectively control the emission of nitrogen oxides. For example, in a typical wet limestone control system, one would expect less than 30 per cent of the nitrogen oxide and nitrogen dioxide to be removed from such conventional wet scrubbers of the type principally designed for controlling sulfur dioxide. Therefore, the wet limestone scrubbing system does not effectively simultaneously control the two general most harmful pollutants associated with fossil fuel fired power plant, i.e., sulfur dioxide and nitrogen oxides.
As far as the removal of nitrogen oxides from fossil fired fuel plants is concerned, there is presently no commercial effluent gas treatment control method. However, there are methods being presently developed for removing nitrogen oxides from effluent gases. Such methods being developed generally related to the use of solid catalytic materials to combine or react with the nitrogen oxides in order to convert them into a chemical form that can more readily be removed from the gas system by conventional means. The feasibility of such solid catalytic materials to remove nitrogen oxides is questionable because of the tendency of such materials to be deactivated by various coatings or poisons. In addition, the cost of catalytic materials is very high and the conversion rate achieved with such is relatively low.